Enhanced Cage Insertion Assembly

ABSTRACT

An inserter instrument for inserting an intervertebral fusion cage having curved sidewalls, comprising:
         a) a threaded securement rod that mates with the cage via screw threads;   b) a cannulated cage holder to receive the rod and hold the cage in position as the sheath is retracted; and   c) a bulleted cannulated sheath,
 
wherein the sheath is curved and comprises a superelastic shape memory material having a curved configuration and a straight configuration.

CONTINUING DATA

This application is a continuation of and claims priority fromco-pending U.S. Ser. No. 14/623,982, filed Feb. 17, 2015, entitled“Enhanced Cage Insertion Device” (Voellmicke) (DEP6325USCNT1), and fromU.S. Ser. No. 12/822,739, filed Jun. 24, 2010, now U.S. Pat. No.8,979,860, entitled “Enhanced Cage Insertion Device” (Voellmicke)(DEP6325USNP), the specifications of which are incorporated by referencein their entireties.

BACKGROUND OF THE INVENTION

The natural intervertebral disc contains a jelly-like nucleus pulposussurrounded by a fibrous annulus fibrosus. Under an axial load, thenucleus pulposus compresses and radially transfers that load to theannulus fibrosus. The laminated nature of the annulus fibrosus providesit with a high tensile strength and so allows it to expand radially inresponse to this transferred load.

In a healthy intervertebral disc, cells within the nucleus pulposusproduce an extracellular matrix (ECM) containing a high percentage ofproteoglycans. These proteoglycans contain sulfated functional groupsthat retain water, thereby providing the nucleus pulposus with itscushioning qualities. These nucleus pulposus cells may also secretesmall amounts of cytokines as well as matrix metalloproteinases (MMPs).These cytokines and MMPs help regulate the metabolism of the nucleuspulposus cells.

In some instances of degenerative disc disease (DDD), gradualdegeneration of the intervertebral disc is caused by mechanicalinstabilities in other portions of the spine. In these instances,increased loads and pressures on the nucleus pulposus cause the cellswithin the disc (or invading macrophages) to emit larger than normalamounts of the above-mentioned cytokines. In other instances of DDD,genetic factors or apoptosis can also cause the cells within the nucleuspulposus to emit toxic amounts of these cytokines and MMPs. In someinstances, the pumping action of the disc may malfunction (due to, forexample, a decrease in the proteoglycan concentration within the nucleuspulposus), thereby retarding the flow of nutrients into the disc as wellas the flow of waste products out of the disc. This reduced capacity toeliminate waste may result in the accumulation of high levels ofproinflammatory cytokines and/or MMPs that may cause nerve irritationand pain.

As DDD progresses, toxic levels of the cytokines and MMPs present in thenucleus pulposus begin to degrade the extracellular matrix. Inparticular, the MMPs (as mediated by the cytokines) begin cleaving thewater-retaining portions of the proteoglycans, thereby reducing theirwater-retaining capabilities. This degradation leads to a less flexiblenucleus pulposus, and so changes the loading pattern within the disc,thereby possibly causing delamination of the annulus fibrosus. Thesechanges cause more mechanical instability, thereby causing the cells toemit even more cytokines, typically thereby upregulating MMPs. As thisdestructive cascade continues and DDD further progresses, the discbegins to bulge (“a herniated disc”), and then ultimately ruptures,causing the nucleus pulposus to contact the spinal cord and producepain.

One proposed method of managing these problems is to remove theproblematic disc and replace it with a porous device that restores discheight and allows for bone growth therethrough for the fusion of theadjacent vertebrae. These devices are commonly called “fusion devices”.

Designs of intervertebral fusion devices are generally either box-like(i.e., Smith-Robinson style) or threaded cylinders (i.e., Clowardstyle). Smith-Robinson style implants have the advantage of possessingbetter contact area to the vertebral endplates, but rely on a coarsesurface texture (such as teeth) to prevent their migration onceimplanted. Insertion then requires over distraction of the disc space toslide the implant in or to provide a smoother implant, which can migratepost-op.

One such box-like design is the Brantigan cage, which is disclosed inU.S. Pat. No. 4,743,256 (“Brantigan”). Brantigan discloses an improvedsurgical method for eliminating spinal back pain caused by ruptured ordegenerated vertebral discs by spanning the disc space between adjacentvertebrae with rigid fusion devices, or “cages”, having surfacesfacilitating bone ingrowth and bottomed on prepared sites of thevertebrae to integrate the implant with the vertebrae and to provide apermanent weight supporting strut maintaining the disc space.

One commercial box-like design is the injection-molded carbon fiberreinforced PEEK (CFRP) cage made by DePuy Spine. However, these cagesare difficult to insert because of the interference fit that is requiredfor intervertebral space distraction. In addition, the reinforced PEEKmaterial that makes up the teeth is brittle and so is susceptible tobreakage when applying impact or torque loads to the implant.

Current interbody devices are made from single materials (e.g., machinedtitanium, or molded and/or machined PEEK). Titanium has the disadvantageof being radiopaque (which can interfere with fusion assessment onx-ray) while also having a high modulus of elasticity (which can stressshield the bone graft). Injection molded CFRP is very brittle andsusceptible to fracture during insertion. Unreinforced PEEK is much lessbrittle but also weaker than carbon-filled PEEK, requiringthicker-walled designs (diminishing space for bone graft). In addition,the teeth of an unreinforced PEEK cage are softer and so may allow moremigration. Both PEEK and carbon-filled PEEK are radiolucent.

U.S. Pat. No. 6,824,565 (“Muhana”) discloses implant and instrumentdesigns wherein some of the implant embodiments have planked designs anda mating inserter instrument. However, the disclosed inserter wrapsaround the exterior of the implant and partially into grooves on theimplant. Moreover, the disclosed implant is derived from bone and is nothollow. The insertion technique disclosed by Muhana requires a cuttingtool to prepare a channel for the implant.

US Patent Publication 2008-0154377 (Voellmicke) discloses a cage adaptedto contain an inserter within its inner volume during insertion.

US Patent Publication 2009-0198339 (Kleiner) discloses an implantableintervertebral fusion cage including a removable means for retainingmaterial inside of the cage during implantation. Embodiments aredirected toward an implantable intervertebral fusion cage that includesat least one removable shield or veneer that is capable of retaining asurgically useful material, such as a spinal fusion-inducing material,inside of the fusion cage during implantation and/or until the shield orveneer is removed. None of the Kleiner shields cover the teeth of thecages.

U.S. Pat. No. 7,569,054 (Michelson) discloses disc space docking anddistraction means. In particular, Michelson discloses an apparatus foruse in human surgery has a tubular member with a passage for providingprotected access to a surgical site. The passage has a minimum widthtransverse to the mid-longitudinal axis of the tubular member. Twoopposed extensions extend from the distal end of the tubular member. Theextensions each have a length and a maximum height perpendicular to thelength. The maximum height of the extensions are less than the length ofeach extension and greater than one-half the minimum width of thepassage. Each extension has an interior surface at least in part facingthe mid-longitudinal axis of the tubular member. The interior surfacesof the extensions are spaced apart from one another along the length ofeach extension a distance no less than the minimum width of the passage.Each extension has opposed bone contacting surfaces configured tocontact portions of bone.

Other relevant instruments include those disclosed in U.S. Pat. No.7,008,431 (“Simonson”); U.S. Pat. No. 5,797,909 (“Michelson II”); U.S.Pat. No. 6,080,155 (“Michelson III”); U.S. Pat. No. 6,096,038(“Michelson IV”); U.S. Pat. No. 7,300,440 (“Zdeblick”); and US PatentPublication 2009-0198339 (“Kleiner”).

In summary, the insertion of both smooth and toothed intervertebralcages has proven to be problematic due to high resistance forces(friction) and interference fit of the cage and intervertebral space.Whereas toothed cages are difficult to insert, cages with smooth upperand lower surfaces have demonstrated undesirable migration.

Current injection-molded PEEK or carbon fiber reinforced PEEK (CFRP)cages are difficult to insert because of the interference fit betweenthe textured/spiked surfaces of the implant and the bony endplates.

The difficulty of direct, unshielded cage insertion and finalpositioning in the disc space also increases the likelihood of bonyendplate damage, as the disc space preparation, FSU distraction forcesand insertion trajectory are variable.

Consistent and accurate placement of the posteriorly inserted spinalfusion cages is difficult because light tamping and impaction areemployed for final positioning. Cages have been over inserted viapushing or impaction through the annulus and into the adjacent bodycavities and/or structures.

Most cages are filled with graft and/or bone inducing substancesincluding BMP and collagen sponge. It has been found that the graftand/or BMP frequently drips or falls out of the graft retaining pockets.The uncontrolled delivery of the BMP/graft can irritate adjacent tissuesand prompt bone formation in undesired locations including heterotopicbone.

Many spinal fusion procedures require either pre and or post packing ofthe disc space, thereby increasing patient risk and operative time.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a cageinsertion instrument adapted to insert an intervertebral interbody cagethrough a conventional spinal surgery approach (such as ALIF, TLIF,PLIF, or LLIF). In preferred embodiments, this instrument includes acannulated sheath comprising a) a proximal cannulated portion, and b) adistal cannulated sheath that surrounds the cage during insertion intothe disc space. The sheath shields the textured surface of the cage fromthe vertebral body endplates, thereby preventing their stress-inducingengagement therewith. The sheath has an expandable tapered or bulleteddistal tip to ease insertion and placement of the instrument (and cage)within the disc space. Once the cage is inserted to its proper depth inthe disc space, the sheath can be retracted while the cage is heldstationary by a threaded rod disposed within the sheath. This retractionexposes the sharp, textured surface of the cage for engagement with thevertebral endplates.

Therefore, the inserter of the present invention provides a number ofbenefits to the spinal surgeon. In particular, it provides initialdistraction of the disc space, improves the ease of insertion andplacement of an intervertebral spacer, minimizes damage to the spacerand/or endplate during spacer insertion and placement, provides a meansto deliver and contain graft within the spacer and surrounding discspace, and reduces the secondary positioning and time required toimplant a spacer.

The sheath also provides a delivery and containment means for bone graftand/or BMP's, bone graft can be placed either within the cage, or distalor proximal to the cage for simultaneous delivery therewith. Thiscontainment means prevents leakage during insertion into the body,during placement into the disc space, and during final deployment intothe disc space.

Therefore, in accordance with the present invention, there is providedan assembly comprising:

-   -   a) an intervertebral fusion cage having a leading end, a        trailing end, an upper face and a lower face, and    -   b) an inserter comprising:        -   i) a cannulated rod holder having a bore therethrough,        -   ii) a rod received within the bore of the cannulated rod            holder, the rod adapted to mate with the cage,        -   iii) a cannulated sheath receiving the cannulated rod            holder, the sheath having a plurality of sheath portions            extending distally therefrom, and            wherein a first sheath portion has an inner portion bearing            against the lower face of the cage, and            wherein a second sheath portion has an inner portion bearing            against the upper face of the cage.

The present invention includes a retractable sheath that holds a cage asit is inserted into the disc space, thereby shielding the sharp teeth ofthe cage from boney endplates and delivering graft to the disc space.Whereas conventional instrument systems that use delivery tubes for thecage do not place the tube into the disc space (but rather between theskin and the entrance to the disc space), the tubular sheath of thepresent invention enters the disc space.

The present invention also includes tubular, expandable spinal discgraft containment means.

Also in accordance with the present invention, there is provided amethod of delivering a fusion cage to an intervertebral disc spacebounded by adjacent vertebral endplates, comprising the step of:

-   -   a) delivering the fusion cage into the disc space without        contacting its surfaces to the vertebral endplates during        delivery.

In preferred embodiments thereof, a sheath is interposed between thecage surfaces and the endplates to prevent contact therebetween duringdelivery.

Also in accordance with the present invention, there is provided amethod of delivering a fusion cage into the disc space, comprising thesteps of:

-   -   a) inserting a distal end of a cannula into an intervertebral        disc space,    -   b) delivering the fusion cage through the cannula into the disc        space.

DESCRIPTION OF THE FIGURES

FIGS. 1A-1D disclose various views of an inserter of the presentinvention having four main components.

FIG. 2 discloses a fusion cage being held by an inserter of the presentinvention, along with the space available therein for graft placement.

FIGS. 3A-3D disclose various views of an inserter of the presentinvention, wherein the sheath has a rectangular cross-section thattracks the cross-section of the fusion cage.

FIGS. 4A-4D disclose various steps by which the inserter of FIGS. 3A-3Dinserts a cage into a disc space.

FIG. 5 discloses an inserter of the present invention having three maincomponents.

FIGS. 6A-6B discloses an inserter of the present invention having twomain components.

FIGS. 7A-7B discloses an inserter of the present invention having acurved distal sheath.

FIGS. 7C-7D discloses the distal and proximal loading of the inserter ofFIGS. 7A-7B.

FIGS. 8A-8D disclose the sequential advance of the curved distal sheathof an inserter of the present invention.

FIG. 9 discloses a distal portion of an inserter of the presentinvention having a modular expanding sheath tip.

FIGS. 10A-10B disclose the insertion of multi-component cages with theinserter of the present invention.

FIGS. 11A-11C disclose a distal portion of an inserter of the presentinvention fitted with various slit sheaths.

FIG. 12A discloses a docking port component of the present inventionhaving distally extending securement teeth.

FIG. 12B discloses a docking port component of the present inventionhaving a distally located adjustable collar.

DETAILED DESCRIPTION OF THE INVENTION

In some embodiments, the instrument comprises two, three, four or morecomponents.

Now referring to FIGS. 1A-1D, there is provided an assembly of thepresent invention in which the inserter has four components: a sheath, acannulated rod holder, a rod and a docking port. In particular, theassembly comprises:

-   -   a) an intervertebral fusion cage 1 having a leading end 3, a        trailing end 5 having a threaded hole 6, an upper face 7 and a        lower face 9, and    -   b) an inserter 11 comprising:        -   i) a cannulated rod holder 13 having a bore therethrough and            a distal end portion 17 having a distal end 18 bearing            against the trailing end of the cage,        -   ii) a rod 22 received within the bore of the cannulated rod            holder, the rod having a threaded distal end 20 mating with            the threaded hole of the cage,        -   iii) a cannulated sheath 19 adapted to receive the            cannulated rod holder, the sheath having a plurality of            sheath portions 23,25 extending distally therefrom,        -   iv) a docking port 33 having a bore therethrough and a            substantially frustoconical distal end 35, wherein the            cannulated sheath is slidingly received in the docking port            and            wherein a first sheath portion 23 has an inner portion 24            bearing against the lower face of the cage, and            wherein a second sheath portion 25 has an inner portion 26            bearing against the upper face of the cage.

In general, the rod is a proximally-handled instrument that mates withthe cage and typically has a distally extending screw thread similar toconventional posterior cage inserters. It is typically called a threadedsecurement rod. Typically, the rod has a threaded distal end, thetrailing end of the cage has a mating threaded hole, and the threadeddistal end of the rod is received in the mating threaded hole of thecage to secure the cage. The threaded connection allows the surgeon tokeep the cage in its inserted position while the sheath is removedtherefrom.

The function of the cannulated rod holder is to hold cage in position assheath is retracted. As shown in FIG. 2, it typically has distallyextending feet 24 for bearing against the trailing end of the cage.Thus, in some embodiments, the cannulated rod holder may be considered acannulated cage holder as well. In some embodiments, the cannulated rodholder can further include a cylindrical flange or “piston” 99 thatextends radially about the distal portion of the rod. This piston allowsfor sealed graft or BMP delivery distally thereof. As shown in FIG. 2,graft materials 31 can be placed within the cage, or placed distaland/or proximal to the cage within the cage holder, thereby eliminatingthe need to pre-pack or post-pack the disc space with graft materials.The piston feature provides a proximal stop for such graft placementproximal of the cage.

Referring back to FIGS. 1A-1D, the bulleted sheath 19 is a retractablecannulated sheath that slides over the rod/rod holder assembly. Thesheath preferably has a very smooth (i.e., low coefficient of friction),semi-rigid inner wall 24,26 with a wall thickness of approximately 0.5mm or less. Preferred materials of construction for the sheath include:polymerics (such as polyethylene, polypropylene, PEEK, polyurethane, andPTFE) or metallics (such as stainless steel, titanium alloy, andnitinol). One preferred sheath is constructed of a radiolucent materialthat allows for fluoroscopic imaging of the cage. In some embodiments,the sheath has a bulleted distal tip that optionally possesses at leastone expansion slot (with four such slots shown in FIGS. 1A-1D, 2 and4A-4D). Now referring to FIGS. 3A-3D, in some embodiments, the sheathcan be produced in varying shapes, including those having a rectangulartransverse cross-section 50.

In use, and now referring to FIG. 2, the sheath typically contains bonegraft 31. In some cases, at least a portion of the bone graft is locatedwithin the cage. In others, at least a portion of the bone graft islocated outside of the cage.

In some embodiments, the sheath comprises a distal pair of cup-like,opposed sheath half leafs, while in others the sheath comprises foursheath quarter leafs. Now referring to FIGS. 6A-6B, the proximal portion98 of each distal sheath leaf 23, 25 is adapted to flex, therebyallowing the distal tip of the distal sheath leaf to open and close. Inpreferred embodiments, in their collapsed arrangement, the distal sheathleaves form a substantially conical shape distally, thereby forming adistal bullet tip. In other cases, the distal sheath leaves form asubstantially tubular sheath shape proximally. In this way, thecollective shape of the distal sheath leaves is much like that of abulleted cage—i.e., it has a tubular body and a bulleted distal tip.

The distal sheath portions can also possess smooth outer surfaces toreduce friction and thereby increase the ease of insertion.

Typically, and now referring to FIG. 3A-3D, the inserter furthercomprises: iv) a docking port 33 having a bore therethrough and asubstantially frustoconical distal end 35, wherein the cannulated sheathis slidingly received in the docking port. The docking port acts as aretractor for soft tissue and helps to place the cannulated sheath uponthe vertebral body or within the disc. The docking port can also controlinsertion angle and depth of the bulleted sheath with enclosed cage. Insome embodiments, the port is a cannulated body having a throughbore anda distal end portion having a tapered, cannulated, pyramidal orfrustoconical shape.

The present invention is believed to be compatible with any conventionalfusion cage. Typically, the upper and lower faces of the cage comprise aplurality of teeth. In some embodiments, the cage has a substantiallyrectangular transverse cross-section and the sheath has a correspondingsubstantially rectangular transverse cross-section. In some embodiments,the cage has a substantially circular transverse cross-section and thesheath has a corresponding substantially circular transversecross-section. In some embodiments, the cage has a substantiallyelliptical transverse cross-section and the sheath has a correspondingsubstantially elliptical transverse cross-section.

Typically, the cage distracts the disc space during insertion. It iseasy to insert and optimizes clinical performance once in place becauseit resists migration and subsidence, has an appropriate stiffness forload sharing, is preferably radiolucent, and has a shape that is able tocontain injected graft material such as growth factors. In addition, thecage is robust over a wide variation of surgical technique because itwill not break even when large forces are applied thereto.

The cage of the present invention is preferably compatible with thebroad use of injectable paste-like bone grafting materials, such asBMP-containing pastes. It may be inserted empty and then filled withgraft in—situ. With the availability of injectable pastes, cages will nolonger require large, contiguous internal volumes to acceptmorselized/granular bone graft. Spaces can be smaller and more numerous.The cage of the present invention will be contained and shielded by thebulleted sheath and will therefore not experience as large impact loadsduring insertion.

Now referring to FIGS. 3A-3D, in some embodiments, the cage has atransverse cross-section 50 that is rectangular, and the transversecross sections of the port, the bulleted sheath and the cannulated cageholder can substantially match that of the cage itself. This is apreferred embodiment, as it minimizes the over-distraction required inother embodiments for cage insertion.

Now referring to FIGS. 4A-4D, in one method of using the four-componentinserter with the present invention, the sequence of implantation stepsare as follows:

-   -   (1) fill the cage and sheath with bone graft.    -   (2) dock the docking port 33 onto the disc space. The port can        be used to direct the angle and location of any desired disc        clearing effort as well as cage implantation.    -   (3) advance of the bulleted sheath. The bulleted sheath 19        containing the graft and cage are advanced to the desired depth        and location. The bulleted sheath reduces insertion forces due        to its shape and its lubricious material of construction, while        encasing the cage and its associated securement features        (teeth).    -   (4) imaging. Imaging is performed to confirm cage positioning.    -   (5) sheath retraction: The sheath is retracted from the cage 1,        thereby exposing the cage and its contents to the vertebral        endplates.    -   (6) Cage Disconnection/Release: Following retraction of the        sheath, the threaded rod is disengaged from the cage, thereby        leaving the cage in the disc space at the desired location.    -   (7) Added Graft Injection (optional): As a last step, additional        graft can be deployed via packing or injecting through the        cannulated cage holder.

Now referring to FIG. 5, in some embodiments, the inserter instrument ofthe present invention is a three-component design that does not have adocking port. This design includes:

-   -   a) a threaded securement rod 22 that mates with the cage via        screw threads in a manner similar to conventional posterior cage        inserters;    -   b) a cannulated cage holder 13 to receive the rod and hold the        cage in position as the sheath is retracted; and    -   c) a bulleted cannulated sheath 19.

In using the inserter of FIG. 5, the bulleted sheath (containing thegraft and the cage 1) is advanced to the desired location. Due to theshape and lubricious material which encases the cage and associatedsecurement features (such as teeth), the bulleted sheath reducesinsertion forces. Imaging is then performed to confirm positioning.

Now referring to FIGS. 6A-6B, there is provided a simple two-componentembodiment of the present invention employing a cage pusher/holder 61and an insertion sheath 19. The cage pusher/holder features the threadedfeature of the rod and the shoulder 63 of the cannulated rod holder ofFIGS. 1A-1D. The cage pusher/holder holds the cage 1 in position assheath is retracted, and the feet can act as a piston for sealed graftdelivery. The bulleted sheath 19 (containing the graft and cage) isadvanced to the desired location. The bulleted sheath reduces insertionforces due to the shape and lubricious material which encases the cageand associated securement features (such as teeth). Imaging is performedto confirm positioning.

In some embodiments, and now referring to FIGS. 7A and 7B, the cages ofthe assembly of the present invention have curved sidewalls. Typically,these curved cages are placed in an anterior portion of the disc space.The curved sheath reduced the need for post-insertion manipulation oftheses cages with conventional insertion methods which is morechallenging due to the final position of the cage and the increasedmanipulation and forces that are required to psuh it in.

In preferred cases, the sheath is curved to help deliver these curvedimplants. In cases in which the sheath is curved, the sheath preferablycomprises a superelastic shape memory material and has a curvedconfiguration and a straight configuration. The sheath of the insertiondevice of the present invention also possesses curved sidewalls 71,72,thereby providing for shielded placement of the curved cage in thedesired final location prior to sheath retraction. In one type ofpreferred curved inserter device (FIG. 7C), there is distal loading ofthe cage, allowing for minimal diameter of the bulleted sheath andcannulated cage holder. The second type of curved inserter device (FIG.7D) allows for proximal cage loading, but requires an increased diameterof the bulleted sheath and cannulated cage holder. Such a curvedinserter can be made to be self-steerable by using a memory metal ormemory polymer sheath, or by using a threaded inserter that recovers itsunloaded position upon deployment from the docking port.

In some embodiments, and now referring to FIGS. 8A-8D, the cage insertercan be steered into its desired location via cables or other means,wherein the sheath 19 has a tensioning cable 75 attached thereto.

In some embodiments, and now referring to FIG. 9, the cage inserter canhave a modular expanding tip 77. The distal tip of the bulleted sheathcan be modular and be attached to the proximal portion of the sheath.The modular component can be prepackaged sterile and marketed with thematching cage size contained within to minimize over-distraction. Theentire inserter can also be polymeric and/or disposable.

In some embodiments, and now referring to FIGS. 10A and B, multiplecages 81 may be deployed. A plurality of curved or straight cages (or acombination of curved and straight cages) of a size smaller than astandard cage can be inserted either in succession or simultaneously. Insome embodiments thereof, multiple cages can be connected to each otherby a cable 83 to provide a more stable construct.

In some embodiments, and now referring to FIGS. 11A-C, the split sheathcomprises a longitudinal gap 91 between sheath portions (i.e., thesheath portions do not contact each other). This gap allows fordifferent cage heights to be handled by the same sheath component,thereby reducing the number of potential instruments in the set.

In some embodiments, and now referring to FIGS. 12A-B, the docking portcould have multiple means for attachment, such as teeth, to providesecurity in between or onto the vertebral bodies. In some embodiments,and now referring to FIG. 12A the docking port can have one or moretongs or spikes 51 extending distally from its distal end portion toassist in holding position upon the vertebral bodies or within the disc.Typically, the docking port also has a proximal handle 53

Now referring to FIG. 12B, the docking port could also include anadjustable collar 93 and incremental adjustment grooves 95. Thesecomponents could be used to both dock onto the vertebral bodies andcontrol the depth to which the instrument is introduced into the discspace.

Typically, the inserter of the present invention can be made out of anymaterial commonly used in medical instruments. The cage insertioninstrument can be made available in a sterile version with preassembledcage and graft, or in a reusable version. If the inserter is designed tobe reusable, then it is preferred that all of its components be made ofstainless steel. If the inserter is designed to be disposable, then itis preferred that at least some of the components be made of plastic.Preferably, at least one component of the inserter is sterilized. Morepreferably, each component is sterilized.

The intervertebral fusion cage of the present invention may bemanufactured from any biocompatible material commonly used in interbodyfusion procedures. In some embodiments, the cage is made from acomposite comprising 40-99% polyarylethyl ketone PAEK, and 1-60% carbonfiber. Such a cage is radiolucent. Preferably, the polyarylethyl ketonePAEK is selected from the group consisting of polyetherether ketonePEEK, polyether ketone ketone PEKK, polyether ketone ether ketone ketonePEKEKK, and polyether ketone PEK. Preferably, cage is made from woven,long carbon fiber laminates. Preferably, the PAEK and carbon fiber arehomogeneously mixed. Preferably, the composite consists essentially ofPAEK and carbon fiber. Preferably, the composite comprises 60-80 wt %PAEK and 20-40 wt % carbon fiber, more preferably 65-75 wt % PAEK and25-35 wt % carbon fiber. In some embodiments, the cage is made frommaterials used in carbon fibers cages marketed by DePuy Spine, Raynham,Mass., USA. In some embodiments, the composite is PEEK-OPTIMA™,available from Invibio of Greenville, N.C.

In other embodiments, the cage is made from a metal such as titaniumalloy, such as Ti-6A1-4V. In other embodiments, the cage is made from anallograft material. In some embodiments, the cage is made from ceramic,preferably a ceramic that can be at least partially resorbed, such as HAor TCP. In other embodiments, the ceramic comprises an oxide such aseither alumina or zirconia. In some embodiments, the cage is made from apolymer, preferably a polymer that can be at least partially resorbed,such as PLA or PLG.

In preferred embodiments, the cage is provided in a sterile form.

We claim:
 1. An assembly comprising: i) an intervertebral fusion cagehaving curved, substantially parallel sidewalls, and ii) an inserterinstrument for inserting the intervertebral fusion cage, comprising: a)a threaded securement rod that mates with the cage via screw threads; b)a cannulated cage holder to receive the rod and hold the cage inposition; and c) a bulleted cannulated, extensible and retractablesheath extending from the cage holder, wherein the sheath is curved andcomprises a superelastic shape memory material having a curvedconfiguration and a straight configuration, wherein the cannulated cageholder holds the cage in position as the sheath is retracted.
 2. Theassembly of claim 1 wherein the sheath comprises curved sidewalls havinga geometry substantially similar to the curved, substantially parallelsidewalls of the cage, thereby providing for shielded placement of thecage in a final location prior to sheath retraction.
 3. The assembly ofclaim 1 wherein the inserter is adapted for distal loading of the cage,thereby allowing for minimal diameter of the bulleted sheath andcannulated cage holder.
 4. The assembly of claim 1 wherein the inserteris adapted for proximal cage loading, thereby allowing for an increaseddiameter of the bulleted sheath and cannulated cage holder.
 5. Theassembly of claim 4 wherein the curved inserter is self-steerable byusing a memory metal or memory polymer sheath.
 6. The assembly of claim4 wherein the curved inserter is made to be self-steerable by using athreaded inserter that recovers its unloaded position upon deploymentfrom a docking port.
 7. The assembly of claim 1 wherein the sheath has atensioning cable attached thereto that allows for steering of theinserter.